pericyklische

Pericyclic is a German adjective meaning "pericyclic". In chemistry, the term "pericyclic" refers to a class of chemical reactions that occur in a concerted, cyclic transition state involving a cyclic rearrangement of bonding electrons. These reactions do not involve any intermediate ions or radicals. The key characteristic of pericyclic reactions is that they proceed through a single transition state where bonds are simultaneously broken and formed. This concerted nature implies that the reaction proceeds without the formation of discrete, high-energy intermediates.

The concept of pericyclic reactions was largely developed by Robert Burns Woodward and Roald Hoffmann, who were awarded the Nobel Prize in Chemistry in 1981 for their work on the conservation of orbital symmetry, which explains the stereochemistry and reactivity of many pericyclic reactions. Common examples of pericyclic reactions include the Diels-Alder reaction, the electrocyclic reactions, and the sigmatropic rearrangements. These reactions are important in organic synthesis due to their predictability, stereospecificity, and the ability to form complex molecules under mild conditions. The Woodward-Hoffmann rules provide a framework for predicting whether a pericyclic reaction will occur thermally or photochemically, based on the symmetry of the molecular orbitals involved.